Is there any allusion to "Climbing Ashes"?

In "A Dream of Red Mansions", when Jiao scolded Jia's family, he said: "... those who crawl on ashes crawl on ashes, and those who raise a brother-in-law raise a brother-in-law." Climbing ashes is a common saying, also called "picking up ashes." It refers to the improper sexual relationship between father-in-law and daughter-in-law.

One theory is that this proverb originated from Wang Anshi's story: Wang Anshi's son passed away in his early years, and his wife was a young widow, so she built a small building to live in. Wang Anshi often visited his daughter-in-law out of concern for her. However, the daughter-in-law misunderstood her father-in-law and thought that Wang Anshi had evil intentions, so she wrote a poem on the wall to express her intentions. Wang Anshi was quite embarrassed when he saw the poem, so he used his nails to scrape off the wall dust. As a result, there is a saying in the outside world of "picking off ashes". Obviously, this legend is far-fetched and was probably fabricated by political opponents to slander Wang Anshi.

Another way of saying it is: "Climb ashes" is a homophone. Climbing ashes will inevitably dirty your knees. "Dirty knees" and "dirty daughter-in-law" are homophonic. This saying originated from Li Yuanfu's "Chang Tan Cong Lu" in the Qing Dynasty: "It is customary to pick off the ashes for those who are sexually immoral to their wives. Gai is a slang term for dirtying a daughter-in-law. The pronunciation of kneeling is the same. Picking up the ashes means dirtying the knees." This statement seems credible. But it’s still hard to justify: “Climbing ashes” is unlikely in life. And why do those who "pick up ashes" necessarily dirty their knees?

Wang Youguang of the Qing Dynasty had another theory. Wang talked about the origin of "grabbing ashes" in "Wuxia Proverbs": In the past, temples were everywhere and the incense was very prosperous. In order to worship ghosts and gods, people often burn large amounts of paper money coated with tin foil. As time goes by, there is more and more tin ash. The temple owner can get a good price by selling the tin ash. When the news spread, profit-seekers often went to temples to steal tin ashes. "Pick up the ashes" means stealing tin. Tin and daughter-in-law have the same pronunciation, so it is regarded as a code word. It seems that Wang Youguang's explanation makes sense. The purpose of "picking up ashes" is to steal tin, and "tin" and "daughter-in-law" have the same pronunciation, so "stealing tin" became "stealing wife", which may be the origin of the term "picking out ashes".